Prior tissue working instruments, suitable for endoscopic surgery, have included a hand piece engagable proximal part and a tissue working distal part, and more particularly have included an elongate, generally tubular outer member in which an elongate inner member is disposed movably for surgically working (e.g. removing, shaping, etc.) tissue.
Early examples of such instruments tended to be rigid and straight. Later examples included instruments having a bent or bendable outer tubular member and an inner elongate member having a length portion of sufficient flexibility to enable tissue working movement (e.g. rotation and/or reciprocation) thereof within the bent outer member.
Typically the proximal end of the outer member is held fixedly to the frame of a hand piece and the movable inner member is movably (e.g. rotatably or reciprocably) driven by a motor unit fixed to the hand piece housing.
By way of example, some prior instruments of this kind use a movably driven inner member which enables surgical detritus, such as typically liquid carrying bits of severed tissue, to be drawn proximally of the tubular inner member toward a suction source connected to the hand piece.
Instruments of this type include so-called shavers or cutters, wherein the inner and outer members have distal tissue working tips having cutting edges relatively movable to shear tissue from the surgical site. Instruments of this type may further include burs in which an inner member distal end carries a bur head with sharp edges movable (e.g. rotatable) to remove bits of tissue from the surgical site. The bur head may be partially guarded by the distal end of the outer member.
In early bent instruments of this general type, the flexible inner member portion at the outer member bend was variously constructed of an elongate helical metal coil, or counter wound coaxial helical metal coils, or a solid metal tube perforated by transverse slots or spaced holes. Difficulties variously included limited usable operating life, limited durability in use, expense and relative complexity of manufacture, and difficulty of sealing against leakage (e.g. of incoming irrigation liquid or outgoing suctioned material) through the wall of the inner tube flexible portion, as the moving inner member flexed.
In time, leading suppliers in the industry introduced movably driven inner tubular members of intrinsically flexible polymer materials, with or without additional fill (particles, strings, etc.) or reinforcing structure embedded therein.
This gave rise to attempts to fix a metal tissue working tip on the distal portion of the polymer tube to try to transmit sufficient torque.
For example, Donahue U.S. Pat. No. 5,282,821 bonds (by adhesive) a cutting tip to a rotor tube which may be of plastic. See also Ryan U.S. Pat. No. 5,282,795 which discloses a reciprocating cutter.
Lim et al. U.S. Pat. No. 5,540,708 in FIGS. 9-11 discloses complexly preformed fingers 125 extending proximally from the cutting tip 110 to be received in corresponding preformed recesses in the distal end of the polymer tube 102 to form a mechanical interlock between the tube and tip. However, the forming and/or machining operations required on the adjacent ends of the tip and tube suggest substantial manufacturing expense.
Anctil U.S. Pat. No. 5,922,003 discloses a metal cutting tip having a reduced outer diameter proximal shank with diametrically opposed axially elongate slots 52, 62, 152, 162, 252, 262, etc. (FIGS. 4-7 and 13-15) or diametrically opposed and longitudinally spaced holes 486 (FIG. 16), wherein such cutting tip shank is inserted into the open distal end of a flexible tube 40 of polymer reinforced by wires 68 (FIG. 8). The result is surrounded by heat shrink tubing. The resulting assembly is heated to cause the polymeric material 66 of the tube to flow and the heat shrink tubing to shrink, thereby forcing the polymeric material to flow radially inwardly into the aforementioned slots or holes formed in the tip shank. Axially mechanically interlocking the tip and tube appears to require relatively complex machining to form the diametrically opposed slots or plural holes and thus make the tip relatively expensive. Further, the several embodiments disclosed all show two circumferentially narrow portions of presumably weaker flowed polymer material sandwiched between circumferentially very wide expanses of presumably stronger metal tip material, which may limit the maximum torque transmittable from the tube to the tip.
Finley et al. U.S. Pat. No. 5,961,532 in FIGS. 11-13 shows a metal tip 40 having a reduced outside diameter proximal portion (annular flange) 61, whose outer periphery is deeply knurled, and a polymer tube 32 having a cylindrical recess 62. Prior to assembly, the tip annular flange 61 is heated and then axially telescoped in the polymer tube recess 62, such that the thermoplastic polymer of the tube plastically flows around the hills and into the valleys of the tip knurl to fix the tube to the tip. Optionally, the tube 62 may be coated with an adhesive, such as epoxy resin, prior to such telescoping. This patent is assigned to the Assignee of the present invention and in general has proved successful in use. However, machining is required to form the tube recess 62 and tip knurl 71. For example, the tip annular flange 61 and tube wall bounding the recess 62 must be of sufficient wall thickness and strength, to avoid distortion or breakage in normal use. However, the depth of the knurl (height from hill top to valley) must be big enough to ensure secure fixation to the polymer tube. In one example in which the outside diameter of the instrument outer tubular member was 4 mm, the thickness of the tip annular flange at the bottom of the knurl valleys was 0.0032 inch (about three one-thousandths of an inch). Thus, relatively high machining precision and hence cost may be required, particularly in smaller outside diameter cutters.
Accordingly, objects and purposes of the present invention include providing a surgical instrument avoiding, or at least reducing negatives of prior devices, and which combines relatively low cost of manufacture with successful operation (including a sturdy fixation of a tissue working tip to a motor driven deformable tubular member). Other objects and purposes of the invention will be apparent to persons of ordinary skill in this art upon reading the following description and inspecting the accompanying drawings.